On the eighteenth of this month [February], we commemorate our Holy Father Leo the Pope of Rome.
The soul of the divine Leo was released,
And demonic hordes he struck with fear.
On the eighteenth Leo released his soul.
Our Holy Father Leo flourished during the reign of Emperor Marcian (450-457). Due to his extraordinary wisdom and purity, and the simplicity and blamelessness of his life, he was ordained Bishop of Old Rome by the grace of the Holy Spirit. He was a venerable shepherd over his flock, and the blasphemies of the heretics he perfectly obliterated in the days of the Fourth Ecumenical Synod, at which six hundred and thirty Fathers gathered in Chalcedon in the year 451. He expounded and dogmatized on many things of the Orthodox faith, and mightily overthrew the doctrines of those heretics who taught the nonsense that Christ our God had one nature, one energy and one will.
Because those who are hated by God fought against the truth, and they actively employed themselves to ravage the divinely inspired doctrines of the divine Fathers, for this reason this blessed man submitted to the request offered by the entire Synod, and he occupied himself for many days with fasting and vigils and prayer. Wherefore inspired by the life-creating Spirit, he set out and lay down in writing concerning the issues that were being discussed. He proclaimed with clarity the two natures and two energies and wills of Christ our God, and by means of a letter he sent it to the above mentioned Fourth Ecumenical Synod. There it was received by the multitude of venerable Fathers gathered together, and it was considered to be a pillar of Orthodoxy, and they believed that it came from the mouth of God. Therefore this Holy Synod rested on this, and they resisted with greater courage the multitude of Monophysites, as well as Monothelites, and it dissolved their intricate wiles. And when that Holy Synod dissolved, the divinely sweet Leo continued to live in this present life, and as a luminary his virtues shined, and he departed to the Lord in deep old age.
Apolytikion in the Third Tone
Thou wast the Church's instrument in strengthening the Church's teaching of true doctrine; thou didst shine forth from the West like a sun and didst dispel the heretics' error. O venerable Leo, entreat Christ our God to grant us His great mercy.
Kontakion in the Third Tone
From the throne of thy priesthood, O glorious one, thou didst stop the mouths of the spiritual lions; thou didst illumine thy flock with the light of the knowledge of God and with the inspired doctrines of the Holy Trinity. Thou art glorified as a divine initiate of the grace of God.